Radio frequency identification tags and radio frequency identification tag systems are known, and find numerous uses. For example, radio frequency identification tags are frequently used for personal identification in automated gate sentry applications protecting secured buildings or areas. Information stored on the radio frequency identification tag identifies the person seeking access to the secured building. A radio frequency identification tag system conveniently provides for reading the information from the radio frequency identification tag at a small distance using radio frequency (RF) data transmission technology. Most typically, the user simply holds or places the radio frequency identification tag near a base station that transmits an excitation signal to the radio frequency identification tag powering circuitry contained on the radio frequency identification tag. The circuitry, responsive to the excitation signal, communicates the stored information from the radio frequency identification tag to the base station, which receives and decodes the information. In general, radio frequency identification tags are capable of retaining and, in operation, transmitting a substantial amount of information--sufficient information to uniquely identify individuals, packages, inventory and the like.
A typical technology for powering and reading a radio frequency identification tag is inductive coupling or a combination of inductive power coupling and capacitive data coupling. Inductive coupling utilizes a coil element in the radio frequency identification tag. The coil element is excited (or "energized") by an excitation signal from the base station to provide power to the radio frequency identification tag circuitry. The radio frequency identification tag coil, or a second tag coil, may be used to transmit and receive the stored information between the radio frequency identification tag and the base station. Radio frequency identification tags relying on inductive coupling are sensitive to orientation of the radio frequency identification tag with respect to the base station since the field created by the excitation signal must intersect the coil element at substantially a right angle for effective coupling. Read ranges for inductively coupled devices are generally on the order of several centimeters. Longer read distances are desirable, and for certain applications, such as electronic animal identification, baggage tracking, parcel tracking and inventory management applications, are necessary.
Another technology for powering and reading radio frequency identification tags is electrostatic coupling such as employed in the radio frequency identification tag systems and radio frequency identification tags disclosed in the above referenced applications. These systems advantageously provide for substantially increased read/write distances over those available in the prior art. Another advantage derived from the use of the systems and tags therein disclosed is that the user need not bring the radio frequency identification tag in close proximity to a base station or to substantially orient the tag with respect to the base station. It is therefore possible to incorporate the antenna elements of the base station into, for example, a doorway or a vestibule, a package conveyer or an article sorting system, and to energize the tag and read the tag information at a greater distance.
To couple either the inductive or electrostatic signals between the base station and the radio frequency identification tag, the tag necessarily includes an antenna having at least one and frequently two antenna elements. Typically, a tag circuit chip and the antenna are electrically coupled and bonded to a tag substrate. The tag dimensions, governed by the tag substrate dimensions, are typically maintained fairly small. Therefore, the antenna is generally size limited. A smaller antenna, however, adversely affects read ranges. Also, the antenna is necessarily formed co-planar with the tag substrate potentially making the tag orientation sensitive. Because it is undesirable and generally impractical to make the radio frequency identification tag larger, effective antenna size remains limited. And, the typical flat tag design also limits the antenna to a flat, orientation sensitive configuration.
In accordance with preferred embodiments of the invention disclosed in the aforementioned United States Patent Application entitled "Radio Frequency Identification Tag Having an Article Integrated Antenna", it is proposed to form the antenna integral to an article. For example, a preferred implementation sees the antenna printed using conductive ink onto a cardboard or paper package. A radio frequency identification tag circuit chip is then secured to the article and electrically coupled to the antenna. In addition, it is proposed to provide radio frequency identification tag chip assemblies. The chip assemblies provide for bonding a radio frequency identification tag circuit chip to a substrate formed to include a conductive pattern. A preferred conductive pattern, as disclosed therein, is formed by printing the pattern onto a paper substrate using a conductive ink. The chip assembly may then be secured to the article and electrically coupled to the antenna via the conductive pattern.
As will be appreciated, alignment of the circuit chip with an antenna printed on the article or with a conductive pattern printed on the substrate is very important for proper operation of the circuit chip. More particularly, the circuit chip must be positioned within about +/-0.125 millimeter (mm) to properly mate the conductive pads on the circuit chip to the antenna and/or conductive pattern. However, typical technologies for printing the antenna and/or the conductive pattern onto paper or paper like materials will yield edge tolerances on the order of +/-1.5 mm. This edge tolerance dimension is larger than a typical circuit chip. Contributing to the imprecise edge tolerance are several factors including edge bleed of the printed pattern and variation in the location of the printed pattern relative to the substrate.
Thus, there is a need for an improved radio frequency identification tag.